There's been an update, at least to the free UK and ROI edition of Navmii, so that real time routing round traffic jams is now offered for free. This caused me to uninstall Here and reinstall Navmii.
So Navmii now competes better with Google Maps which allows download of limited area to give you data-free navigation. Navmii beats Google now by being able to hold all UK mapping, so no data needed when driving.
To those who will post the Navmii uses Openstreetmaps which is less accurate and it'll send you on a 2 hour trip round the houses, well yes, but you should always review your route first using the processor inside your head!